Lateral stranded tie cables 5

[TRAVIS PUCHERT]

My neighbour has illegally installed 17x 3 strand lateral tie cables in my property, total length of each cable is 14m. The lateral cables are permanent and hold up a retaining wall 10m high x 20m long. An underground garage structure has been built against the retaining wall, but the tension on the cables have not been released/de tensioned.There are three rows of lateral anchors at various depths.Is my ground that these anchors are installed in still under tension/ pressure? In other words, are the 17 x lateral ground anchors still supporting the retaining wall and would the foundations of my house that are in close proximity to the lateral cables be in danger of sagging/ subsidence? The soil is clay and is layered and classified as slip and subsidence.
Many thanks
Travis

 

[PEinc]

I would not worry. unless these strand tieback anchors are intended to be permanent anchors, i.e., they will always be needed to support the underground garage structure's walls. If they are permanently needed, they contractor or owner of the new garage should have gotten your permission and a legal, permanent underground easement which would restrict you ability to disturb the area around the tieback anchors. If the anchors were temporary, but left-in-place anchors that were needed to support a temporary sheeting wall, they will not hurt or affect your structure or property. If, in the future, you need to dig in the area of these abandoned, temporary anchors, the strands will not pose a problem or be a danger. Any tension load that is currently in the strands, will be slowly relieved as the soil overburden is being removed. In addition, if the excavating equipment (backhoe?) digs into a tensioned anchor, the strands will be broken while still confined by soil. No one will be hurt. Even though these temporary tieback anchors probably are not a problem, the contractor should have gotten, and maybe paid for, your permission to drill them across the property line into your property.

http://www.PeirceEngineering.com

 

[TRAVIS PUCHERT]

Thank you for your reply, much appreciated.

Since the tension has not been released on the stranded anchors( therefore they are permanent anchors) and my neighbour has cast the anchor plates and walers in concrete( see photo), which forms part of his garage wall, the question I have is what is still keeping the retaining wall in place. Is it the stranded anchors which are grouted/installed in my property, or is it the new garage structure that is keeping the retaining wall in place, or both?

If it is the anchors that are keeping the retaining wall in place, what impact does this have on my ground and foundations which are +/- 1m away from the stranded cable bulb?

Many thanks

Travis

 

[oldestguy]

Double posting is not allowed here. I answered your other post with "get a professional geotechnical engineer because this case likely may well go to court. However, keep both posts up for a while and then delete the one that gets least response.Edit: Looking at the photo it is quite obvious your neighbor is an amateur, probably never did this sort of thing before. I'd waste no time getting that experienced geotech civil engineer on your side. Another edit: Photo shows a date for last year. It still is not too late to see about legally protecting yourself from damage down the road probably by the geotech preparing a report and an attorney doing the necessary paper work.

 

[TRAVIS PUCHERT]

Thanks oldestguy for info and posting procedures, I am new to this.

 

[PEinc]

"Since the tension has not been released on the stranded anchors( therefore they are permanent anchors" They are permanent only in the sense that they have not been removed and were not detensioned. They are not needed to be permanent if the new garage wall was designed to carry the lateral loads. If so, the anchors are "temporary, but abandoned-in-place" anchors. Permanent anchors would need extra corrosion protection, require a permanent easement, and would be needed to carry all of the lateral earth and surcharge loads for the life of the garage.

By your photo, these look like temporary tieback anchors, without any corrosion protection on the anchor heads. Also, grouted strand anchor do not have a grouted "bulb."

http://www.PeirceEngineering.com

 

[PEinc]

I just read your other thread. If your garage is only 1m away from the 10-11m high anchored wall, construction of the anchored wall could easily have caused settlement and/or lateral movement of your garage. Anchored walls are usually considered to be flexible walls. Flexibility means lateral deflection or movement, which can cause settlement. Your building is close enough to the anchored wall and excavation that it needed to be underpinned or supported by an extra stiff, conservatively designed, sheeting wall. From the photo you posted in your other thread (Note: double posting not allowed), I can't tell how conservative the anchored wall design was. Installing the top row of anchors near the top of the wall is conservative and a good start. However, the wall design is not the only consideration. Settlement or movement of your building could have been caused by drilling tieback anchors and/or soldier beams without temporary casing to prevent lost ground. Another cause of settlement or lateral movement could be one or more of the tieback anchors not holding its/their load and creeping, which causes the anchored wall to move away from your property.

http://www.PeirceEngineering.com

 

[TRAVIS PUCHERT]

Thank you PEinc for your answer, you have clarified a lot for me, it all makes sense.

The cracking and movement I have experienced on my garage structure is due to the garages founding ground settling as a result of the earth being disturbed by the piling and lateral ground anchors. Do you think this could have been aggravated by the delay in the third row of lateral anchors being installed? There was a delay of +/- 8 weeks before the third row of lateral ground anchors were installed and tensioned up, and the piles in this portion( P1-P6, in photo attached) were only 10m long, so with the excavation, this left only 3-4m in the ground. I have also attached a photo of the third row of lateral ground anchors.

 

[TRAVIS PUCHERT]

Please find attached the photo as mentioned in my post above, regarding piles P1 -P6

 

[oldestguy]

As with most structures, reinforcements, etc. In order to develop forces, such as those against a retaining wall, there usually has to be some movement. In this case likely in addition or due to it, the tension in the tie backs some movement would be likely. Exactly what caused it, in this case, is likely a combination of several zones loaded laterally. Your experience with openings, etc. is not unexpected. In any case monitor the movements with a written record and be prepared for more. If this some day turns out to be a claim against the neighbor, you should be prepared to see experts on the contractor's side such as those on this group with many years of experience. I'd do that now, rather than later. Experts locally may not wish to be involved if the contractor has a long time of business in your locality.

 

[PEinc]

Your photos show a very rocky retained excavation face. I would not expect any significant wall or soldier beam movements or lost ground in the rock. Possibly the upper portion of the retained ground, near the top tier of anchors, is soil. Maybe those upper tiebacks were drilled without using casing and some upper soil was lost causing settlement. The wall designer was smart enough to know that pipe pile soldier beams would be appropriate for the rocky ground conditions.

Given the rock visible in the photos, I wouldn't expect that a delay installing the 3rd tier of anchors would cause your problem.

The lower portion of the anchored wall has no lagging, shotcrete, or wire mesh to prevent loose pieces of rock from falling out. This is more of a safety problem for workers in the excavation, along the wall, than for your property and building. I would look to your problem being caused by lost ground during uncased, tieback installation or to upper loose soils consolidating due to vibrations during installation of the tiebacks and/or pipe pile soldier beams. One other possible cause is if there was ground water running across the top of the rock during excavation which caused loss of soil from beneath your building when the excavation was made for installing the shotcrete and the second tier of tieback anchors.

http://www.PeirceEngineering.com

 

[oldestguy]

PRinc comments appear valid. However, I have a question. Is this site in Canada, possibly near Toronto? If so action of glaciers on dolomites or some shales may explain the weak characteristics evident. Edit: A question came to mind tonight. I wonder if there is any problem waiting until damage appears significant enough to make a claim or a notice anyhow. Might the neighbor and his legal advice then say "You saw this movement happening early on and did nothing about it. Thus you are pretty late now trying to make up for a mistake that should have been addressed much earlier". The least I would do is complain about anchoring on my land without a notice or agreement.

 

[EireChch]

As with most structures, reinforcements, etc. In order to develop forces, such as those against a retaining wall, there usually has to be some movement. In this case likely in addition or due to it, the tension in the tie backs some movement would be likely.

If these are prestressed anchors then movement of the wall is not required to mobilise the anchor capacity. It is mobilised after lock off.

I think it is hard to know what the cause of settlement is. PEinc reckons that it could be uncased drilling of anchors, I agree, however if the contractor has construction records that show casing was used in all anchors so there was no loss of soil during drilling. That would kill that argument? I think the wall installation and 1m proximity to your garage is the biggest contributor. Edit: following confirmation of installation with an impact hammer, vibration during driving of pipe piles would have likley induced some settlement.

It looks like a poorly constructed wall based on the shotcreting of the upper portion. Exposed rebar etc. Unless they are planning a 2 layers system of shotcrete which I understand is common in the US? Not so much in other parts of the world. I also think the piles look a little thin? They look to be less than 300mm? I would have expected 450mm. However, without know ground conditions, loading etc. its hard to assess whats suitable.

I strongly agree with OG to start monitoring and get a geotech expert involved straight away.

 

[TRAVIS PUCHERT]

The site is in the South of France, 10km inland from CANNES. The area is zoned seismic, and the soil is clay, high moisture content, stratified layers of rock and is zoned for possible subsidence and collapse.

The piles are 100mm dia steel piles, driven into the ground using the impact method

The anchors are uncased, 3 cable strands per anchor, F=7000kg per cable, 5m unbonded and 8m bonded length

 

[PEinc]

"stratified layers of rock and is zoned for possible subsidence and collapse." From my looking at the pictures, I am surprised that the pipe piles could be driven in such rocky conditions. I can't imagine that the pipe piles drove easily and without significant vibrations. Perhaps this driving effort caused some subsidence and collapse? In the USA, pipe pile soldier (often 150mm to 300mm diameter) beams are often drilled-in when the ground has cobbles, boulders, or rock. IMHO, 100mm piles are probably too small and 450mm piles are probably too big, considering that there are 3 tiers of tieback anchors. When saying that "the anchors are uncased," do you mean that the finished anchors have no casing or do you mean that they were drilled without temporary casing? Are there records of how much grout was pumped into each drill hole? If the amount was excessive, it could indicate lost ground, collapse, or voids behind the wall.

http://www.PeirceEngineering.com

 

[oldestguy]

Quote PEinc. "I am surprised that the pipe piles could be driven in such rocky conditions." This tells me the rock is highly weathered and pretty darn loose. The last photo shows that. Sure the grouting and tensioning the tie-backs can do some improvement, but significant questions can remain. Crossing the fingers and hoping is not an option.

 

[TRAVIS PUCHERT]

Hi PEinc,
regarding the anchors, the holes were drilled without temporary casing. See attached photo of one of the cables used with its outer sheath. I do not know how much grout was installed.

 

[PEinc]

My first tieback anchor job, of many hundreds of jobs, was back in 1975 or 1976. Permanent tieback anchors usually are grouted inside a corrugated plastic sleeve. The corrugated sleeve that your photo shows looks very small in diameter. The smallest corrugated sleeve that I have ever seen and used is 2 inches. I can't tell diameter or length from your photo. However, I do not see any unencapsulated stressing length of bare strands. Also, your photo shows relatively short lengths of corrugated plastic. I assume that steel strands are inside. Your photo does not provide any answers - only more questions. From your other photos, the anchors appear to be temporary anchors that would almost never have plastic encapsulation. You need to find out if the anchors are indeed temporary or permanent. If permanent, you would have a bigger problem. Just because you do not see any drill casing in your photos, that does not mean that casing, temporary or permanent, was not used.

Because the "anchors" in your photo are coiled and not straight, they cannot have already been grouted inside the corrugated sheath. Therefore, there would need to be a sacrificial grout tube also inside and protruding out the top end of the corrugated sheath so that the grout could be tremie pumped to the bottom end of the anchor, inside the sheath, after it has been installed inside the drill hole. I don't see any grout tube. An additional, reusable grout tube would be inserted with the sheathed anchor tendon so that the drill hole could be tremie grouted around the corrugated sheath so that it could bond the anchor to the soil or rock. Look at anchor material details on Williams Form Engineering's web site.

http://www.williamsform.com

http://www.PeirceEngineering.com

 

[Mad Mike]

My gut feeling is that any loss of ground associated with the anchor installation would pale in comparison with the vibrations of pile driving through weathered bedrock just 1m away from your structure.

I would also expect the cracking induced by pile driving to show up immediately, and not worsen to any significant degree over time. If your cracks continue to widen with time, this is more likely due to loss of ground. Alternatively, your foundations are seated on an upper rock layer which has been shaken and re-orientated by the pile driving, such that loss of ground is now occurring through open fractures in this disturbed rock.

Whatever the case, any contractor driving piles immediately adjacent your structure should have (and would have) known to photograph your structure before driving...see if you can get hold of those photos, which would be hard evidence that your structure was not cracked prior to construction commencing.

Find out if your neighbour would be willing to pay for your underpinning and crack repair, amicably...but first be absolutely sure that those were not old cracks that simply opened a little more during construction.

All the best,
Mike

 

[Ron]

Going back to OG's sage advice....get a local geotechnical engineering involved...NOW.